Transcript Biology-of-tooth-movement

Controlling factors:
At the time the primary
second molars are lost. Both
the maxillary and mandibular
molars tend to shift mesially
into the leeway space. but the
mandibular molar normally
moves mesially more than its
maxillary counterpart.
a characteristic of the
growth pattern at this age is
more growth of the mandible
than the maxilla, so that a
relative deficient mandibule
gradually catches up.
Biological Basis of
Orthodontic Therapy
Dr. Manar K Alhajrasi
BDS,MSC,SBO,M.Orht.
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Contents
Tooth supporting tissues
PDL-structure and function
Role of PDL – eruption & stabilization
Response to orthodontic force
Biologic basis of tooth movement
Biologic electricity
Pressure-tension
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Contents
How teeth move clinically-Concepts of optimal force
Effects of force distribution and types of tooth
movement
Force duration and decay
Effects of drugs
Root resorption in orthodontic tooth movement
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Tongue are usually not balanced. In some areas, as in the
mandibular anterior, tongue pressure is greater than lip
pressure. In other areas, as in the maxillary incisor region, lip
pressure is greater. Active stabilization produced by metabolic
effects in the PDL probably explains why teeth are stable in the
presence of unbalanced pressures that would otherwise cause
tooth movement.
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The Periodontium
Orthodontic force ⇆ Changes in the supporting structure.
Periodontium is a connective tissue organ covered by epithelium,
that attaches the teeth to the bones of the jaws and provides a
continually adapting apparatus for support of teeth during
function.
PDL = cells + fibers + tissue fluid
4 connective tissues
Two fibrous
- Lamina propria of the gingiva.
- Periodontal ligament
Two mineralized
-Cementum
-Alveolar bone
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Gingival fibers
Circular fibers
Dentogingival fibers
Dentoperiosteal fibers
Transseptal fibres (Accesory fibres)
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PDL
Progenitor cells
Synthetic cells
a) Osteoblasts
b) Fibroblasts
c) Cementoblasts
Fibres
-Collagen
-Oxytalan
Ground Substance
-Proteoglycans
-Glycoproteins
Resorptive cells
A) Osteoclasts
B) Fibroclasts
C) Cementoclasts
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PDL
Constant remodeling- fibers, bone & cementum.
Principal fibres 1. Alveolar crest group
2. Horizontal group
3. Oblique group
4. Apical group
5. Trans-septal group
Tissue fluidDerived from the vascular system
Acts as Shock absorber-retentive chamber with
porous walls.
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Normal function
Heavy forces- > 1 sec-force transmitted to bone
Bone bending
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Pressure / Force
Short duration
PDL- Adaptive
Prolonged force
Remodeling of
adjacent bone
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Role of PDL
Implications:
Continued eruption
Active stabilization- threshold for orthodontic
force.( 5- 10 gm/cm2 )
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Theories of tooth movement
Pressure- Tension theory
Fluid –Dynamic theory –Bien
Squeeze- Film effect
Oxygen tension
Bone bending theory
Neither incompatible nor mutually exclusive
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Bone Bending
Farrar- (1888) was the first to suggest-alveolar bone
bending plays a pivotal role- tooth movement
Orthodontic appliance is activated- forces delivered
to the tooth are transmitted to all tissues near force
application- bend bone
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Biologic electricity
2 types of electric signals
Piezoelectricity
Electric current flows- electrons are displaced
from 1 part of the crystal to the other.
Bioelectric Potential
Unstressed bone
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Piezoelectricity
Piezoelectricity is a phenomenon observed in many
crystalline materials in which a deformation of the
crystal structure produces a flow of electric current
as electrons are displaced from one part of the
crystal lattice to another
Bone- Organic crystal
Quick decay & equal & opposite signal
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Biologic electricity
Zeev Davidovitch – 1980
Applied electric currents to bone- 15 μ amps combined
force ( 80 g)
Enhanced bone resorption near the anode & bone deposition at
the cathode compared to controls
Orthodontic tooth movement accelerated
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Biologic electricity
ObservationsThe application of PEMF – increased both rate & final
amount tooth movement
Histologic evidence- increase amount of bone deposition &
more osteoclasts
Increased protein metabolism-indicated by creatinine,
creatinine phosphokinase, uric acid.
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Pressure-tension
Sandstedt (1904), Oppenheim (1911),and Schwarz
(1932).
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Classically:
This hypothesis explained that, on the pressure side, the PDL
displays disorganization and diminution of fiber production.
Here, cell replication decreases seemingly due to vascular
constriction.
On the tension side, stimulation produced by stretching of
PDL fiber bundles results in an increase in cell replication
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Fluid Dynamic theory
Force of longer duration- interstitial fluid squeezed
out
Vascular stenosis – decreased oxygen levelcompression
Alteration in the chemical environment
Alterations in the blood flow- changes the chemical
environment
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Cytokines
Named based on presumed targetsLeukocytes- Interleukines
Maintained original names-eg. G-CSF
IL, IFNs,TNF,CSFs,GFs & Fractalkines (chemokine
family)
1980s- cytokines were produced by osteoblasts &
fibroblasts- normal physiologic turnover.
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Effects of force magnitude
Frontal resorption
Hyalinization
Undermining resorption
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Effects of force magnitude
Frontal resorption- Cells attack the adjacent lamina
dura
The osteoblasts lag behind in differentiation-PDL
space enlarges- further initiate osteoclast
remodeling
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Effects of force magnitude
Heavier force- The
blood vesselsexcessively
compressed and
occlude
Sterile necrosis- tissue
injury = Hyalinization
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Effects of force magnitude
Vascular circulation impededdec. celluar differentiationdegradation of cellular and
vascular structures
Glass like structure (1-2mm) -
Hyalinization
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Effects of force magnitude
Undermining resorptionHyalinization- remodeling of
bone around Necrotic connective
tissue-derived from adjacent
undamaged area
Osteoclasts appear – adjacent
bone marrow spaces- attack on
underside of bone next to necrotic
area
Inevitable delayCell differentiation
Considerable thickness to be removed
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Force distribution & Type of tooth
movement
Optimal force-The amount of force & the area of
distribution
The force distribution varies with the type of tooth
movement
Tipping -
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Force distribution & Type of tooth movement
Forces should be kept low- high concentration of
forces
Destruction of the alveolar crest
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Force distribution & Type of tooth movement
Bodily tooth movement-uniform loading of the teeth is
seen.
To produce the same pressure-same biologic responseforce required is twice
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Force distribution & Type of tooth movement
Torque-Initially- Pressure
close to middle region-PDL
wider at the apex
Later part-apical region
begins to compress
Rotation-2 pressure &
tension sides
Tipping – some hyalinization
does occur
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Force distribution & Type of tooth movement
Intrusion-very light forces-concentrated in a small
area
Stretch- principal fibres
Extrusion-Only areas of tension
Light forces- could loosen teeth considerably
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Optimum forces for various tooth
movements-Proffit
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Force Duration
Sustained force- cyclic nucleotides appear- only
after 4 hours
Longer & constant the force- faster the tooth
movement
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Type force duration-force decay
Teeth move in response to force- force changes
May drop to zero
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Type force duration-force decay
Intermittent force- abrupt decline to zero
Removable appliances( HGs), elastics
Tooth movement occurs-Forces decline (interrupted)
Force removed- tooth moves back to tension side
The PDL-improved circulation- formative changes occur
semihyalinization
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Type force duration-force decay
Continuous forceLight- frontal resorption
Heavy- undermining resorption- constant-further
U.Resorption
Destructive to the PDL & tooth
Force decayLight force-FR- no movement till activation
Heavy–UR- force drops-repair & regeneration occurs
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